1. Field of the Invention
The present invention relates to a laminated electronic component and a method for manufacturing the same, and more particularly relates to a laminated electronic component, which includes external electrodes directly provided on external surfaces of a laminate by plating, and to a method for manufacturing the same.
2. Description of the Related Art
As shown in FIG. 11, a laminated electronic component 101, represented by a multilayer ceramic capacitor, includes a laminate 105 including insulating layers 102 laminated to each other and layer-shaped internal electrodes 103 and 104 which are arranged along interfaces between the insulating layers 102. Ends of the internal electrodes 103 and ends of the internal electrodes 104 are exposed at one end surface 106 and the other end surface 107 of the laminate 105, respectively, and external electrodes 108 and 109 are arranged so as to be electrically connected between the ends of the internal electrodes 103 and between the ends of the internal electrodes 104, respectively.
When the external electrodes 108 and 109 are formed, paste electrode layers 110 are first formed by applying a metal paste including a metal component and a glass component on the end surfaces 106 and 107 of the laminate 105, followed by firing. Next, on the paste electrode layers 110, first plating layers 111 primarily composed of, for example, Ni are formed, and second plating layers 112 primarily formed of, for example, Sn are further formed thereon. That is, each of the external electrodes 108 and 109 is formed to have a three-layered structure including the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
When the laminated electronic component 101 is mounted on a substrate using solder, the external electrodes 108 and 109 must have good wettability to the solder. At the same time, the external electrode 108 must provide electrical connection between the internal electrodes 103, which are electrically insulated from each other, and the external electrode 109 must provide electrical connection between the internal electrodes 104, which are electrically insulated from each other. The second plating layer 112 ensures the solder wettability, and the electrical connections between the internal electrodes 103 and between the internal electrodes 104 are provided by the respective paste electrode layers 110. The first plating layer 111 prevents being lost by solder during solder bonding.
However, the paste electrode layer 110 has a relatively large thickness of several tens to several hundreds of micrometers. Thus, when this laminated electronic component 101 is formed to have dimensions within predetermined standard values, in order to ensure the volume of the paste electrode layers 110, an effective volume necessary to obtain electrostatic capacitance must be unfavorably decreased corresponding to the volume of the paste electrode layers 110. On the other hand, since the thicknesses of each of the plating layers 111 and 112 are approximately several micrometers, when the external electrodes 108 and 109 are formed of only the first plating layer 111 and the second plating layer 112, a larger effective volume necessary to obtain electrostatic capacitance is ensured.
For example, in Japanese Unexamined Patent Application Publication No. 2004-146401, a method is disclosed in which a conductive paste is applied to at least edge portions of end surfaces of a laminate in the lamination direction of internal electrodes so as to be in contact with extraction portions of the internal electrodes, this conductive paste is then formed into conductive films by firing or heat-curing, and electroplating is further performed on the end surfaces of the laminate to form electroplating films so as to be connected to the conductive films on the edge portions. According to this method, the thickness of the external electrode at the end surface can be decreased.
In addition, in Japanese Unexamined Patent Application Publication No. 63-169014, a method is disclosed in which conductive metal layers are deposited by electroless plating on entire sidewall surfaces of a laminate at which internal electrodes are exposed so that the internal electrodes exposed at each sidewall surface are short-circuited to each other.
However, with the method for forming external electrodes disclosed in Japanese Unexamined Patent Application Publication No. 2004-146401, although the exposed internal electrodes can be directly connected to the respective electroplating films, since it is necessary to ensure electrical connection of the extraction portions of the exposed internal electrodes before the electroplating is performed, conductive portions must be formed using a conductive paste. A step of applying this conductive paste at specific locations is very complicated. Furthermore, since the thickness of the conductive paste is relatively large, the effective volume rate is disadvantageously decreased.
In addition, in the method disclosed in Japanese Unexamined Patent Application Publication No. 2004-146401, if the conductive paste is not formed, since the ends of the internal electrodes of the laminate are withdrawn from the exposed surface before the plating is performed, a problem may arise in that electrically conductive media are not likely to be in contact with the internal electrodes during the electroplating. In this case, not only is the plating efficiency considerably decreased, but the uniformity of the plating layer is also degraded, thereby resulting in a degradation of humidity resistance of a laminated electronic component.
According to the method disclosed in Japanese Unexamined Patent Application Publication No. 63-169014, since the plating film is formed by an electroless plating method, problems arise in that the rate of forming the plating film is very low, and the density of the obtained plating film is low. In order to improve the above situation, a method in which a catalytic substance, such as Pd, is formed before the plating film is formed may be used. However, when this method is used, a problem arises in that the process becomes complicated. In addition, another problem arises in that the plating film is liable to be deposited at a location other than a desired location.